66. QoS Notes
Quality of Service (QOS)
tools that networking devices use to apply different treatment to packets in the network
to give better service to some and worse to others
Controls, Segments and Discriminates packets in network
4 Characteristics of Network Traffic
1. Bandwidth
speed of the link
capacity of the link
maximum amount of data per second
instantaneous capacity
2. Delay
can be:
one way delay
two way delay
latency in milliseconds
roudtrip of packet in time (ms)
3. Jitter
vatriation in one way delay for consecutive packets sent
4. Loss
amount of loss messages (packets)
In percentage of packets sent
Reasons:
faulty cabling, poor WAN services
queues full, network devices discards packets
3 Types of Traffic
1. Data Traffic
Quality of Experience (QoE)
*Interactive
needs good QoE
example: video and audio conferencing
delay and jitter is important
*Non-Interactive
downloading and uploaing of files
bandwidth is important
2. Voice Traffic
how voice traffic works:
1. users make a phone call
SCCP is the voice signalling protocol used in voice traffic
2. codec digitizes voice to create binary data
voice is a webform
popular voice codec is G.711
gets sample for evry 20ms worth of voice data
voice payload is the data 20ms digitize
payload is worth 160bytes with 40 bytes IP header a total of 200 bytes per 20ms
alotting bandwidth for voice traffic needs to be computed basing on the number of users
and the codec used
tho voice traffic need low bandwidth, it needs stable and low delay, jitter and loss
classified in two:
*Interactive
*Non-Interactive
3. phone places data into packet
4. phone sends packet to destination phone
Guideline for quality voice traffic:
*Delay (One way) = 150ms or less
*Jitter = 30ms or less
*Loss = 1% or less
3. Video Traffic
like voice traffic but needs a higher bandwidth
Guideline for quality voice traffic:
*Bandwidth: 384kbps to 20+ Mbps
*Delay (One way) = 200 - 400ms
*Jitter = 30 - 50ms
*Loss = 0.1 - 1%
Classification and Marking
A. Classification of packets
2 Ways:
1. Classifcation using ACLs
depends on the encapsulation headers:
*source IP
*destination IP
*source protocol
*destination protocol
*destination ports
very general technique and not effective
2. NBAR (Network Based Application Recognition)
solution is to use Deep Packet Inspection (DPI) which enables to look into the payload / data content
with DPI, it enables the device to be application-aware
protocols and application that the NBAR can classify would be based on the
IOS version and model of the router (cisco)
B. Markings
where do we put markings:
A. we can mark layer 2 frames
markings are inserted on the User Priority fields of the ethernet frame header
ISL and 802.1Q headers which are trunking encapsulations
call this markings as COS - Class of Service
marking can be done when frame passess to a trunk port
model and IOS installed on a switch and router varies on its capability to read
L2 and L3 markings.
when a mark L3 packets passes to a switch that do not support L3 markings
the router can translate that L3 marking (DSCP) to COS value (translate/mapping) so the switch can inspect it. Translation can be done vice versa.
Trust Boundary = point in the network where the received COS and DSCP markings can be trusted